A solid catalyst component that contains magnesium, titanium, an electron donor compound, and a halogen as essential components has been used when polymerizing an olefin (e.g., propylene). Various processes have been proposed for polymerizing or copolymerizing an olefin in the presence of an olefin polymerization catalyst that contains the solid catalyst component, an organoaluminum compound, and an organosilicon compound. A polymer produced by utilizing such a catalyst has been used for various applications (e.g., molded products for vehicles and household electric appliances, containers, and films). These products are produced by melting a polymer powder obtained by polymerization, and molding the molten polymer using a molding machine. When producing a large injection-molded product, the molten polymer may be required to have a high melt flow rate (MFR). When producing a desired amount of copolymer in a copolymerization reactor, and directly producing an olefin-based thermoplastic elastomer (TPO) in the reactor without adding another copolymer (i.e., production of a reactor-made TPO by direct polymerization) in order to reduce the cost of a high-performance block copolymer used as an automotive material, a melt flow rate of 200 or more may be required in the homopolymerization stage in order to produce a product that has a high melt flow rate and facilitates injection molding. Therefore, studies have been extensively conducted aimed at increasing the melt flow rate of the resulting polymer. The melt flow rate of a polymer varies depending on the molecular weight of the polymer. When polymerizing propylene, hydrogen is normally added as a molecular-weight modifier. A large amount of hydrogen is normally added when producing a polymer having a low molecular weight (i.e., high melt flow rate). However, the amount of hydrogen that can be added is limited since the pressure that can be applied to the reactor (particularly a bulk polymerization reactor) is limited taking account of safety. When using vapor-phase polymerization, the partial pressure of monomers must be reduced when adding a large amount of hydrogen. In this case, the productivity decreases. Moreover, cost increases as a result of using a large amount of hydrogen.
For example, Patent Document 1 (WO2006/129773) discloses an aminosilane compound shown by R12Si(NHR2)2 as an external electron donor compound used when polymerizing an olefin. Patent Document 1 discloses that a polymer having a high melt flow rate is obtained with a reduced amount of hydrogen by utilizing the aminosilane compound. However, when using the aminosilane compound disclosed in Patent Document 1 as an external electron donor compound when polymerizing an olefin, it is necessary to use a large amount of the aminosilane compound in order to obtain a polymer having desired properties. Therefore, the aminosilane compound disclosed in Patent Document 1 is industrially disadvantageous from the viewpoint of cost. Moreover, the stereoregularity of the polymer decreases although the MFR of the polymer is improved.
Patent Document 2 (JP-A-2007-326886) discloses an olefin polymerization catalyst component that contains a solid catalyst component and an organoaluminum compound, the solid catalyst component being produced by causing a vinylsilane compound and an organosilicon compound shown by [R1R2N]Si(OR3)3 to come in contact with a solid component that contains titanium, magnesium, and a halogen as essential components. Patent Document 3 (JP-A-2007-326887) discloses an olefin polymerization catalyst component that contains a solid catalyst component and an organoaluminum compound, the solid catalyst component being produced by causing a vinylsilane compound, an organosilicon compound shown by [R1R2N]Si(OR3)3, and an organosilicon compound shown by R4R5aSi(OR6)b to come in contact with a solid component that contains titanium, magnesium, and a halogen as essential components. These catalysts aim at producing a polymer having an improve MFR without using an external electron donor compound by causing a significantly small amount of aminosilane compound (as compared with the amount used during polymerization) to come in contact with the solid catalyst component that contains magnesium and titanium. However, it is difficult to produce a polymer having a high MFR using these catalysts. Moreover, a decrease in polymerization activity and stereoregularity of the polymer occurs.
Patent Document 4 (WO2007/026903) discloses an olefin polymerization catalyst component that contains a solid catalyst component and an organoaluminum compound, the solid catalyst component being produced by causing an organosilicon compound shown by [CH2═CH—(CH2)n]qSiR14-q to come in contact with a solid component that contains magnesium, titanium, and a halogen as essential components. High polymerization activity during polymerization is achieved by this catalyst. However, it is difficult to produce a polymer having a high MFR using this catalyst.